arm64: defconfig: enable cpufreq support for RPi3

This enables both the new firmware clock driver and cpufreq driver
available for the RPi3 family of boards.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Acked-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Stefan Wahren <wahrenst@gmx.net>